The present invention relates to a plasma display device comprising a plasma display panel (hereinafter abbreviated to xe2x80x9cPDPxe2x80x9d) and a control method of applying voltage on the plasma display device.
A plasma display device comprising a PDP has recently been developed as a low-profile large screen color display device.
An AC planar plasma display panel with three electrodes shown in FIG. 10 is widely developed at present. In the AC planar plasma display panel with three-electrodes, a pair of glass substrates, i.e., a front panel 1001 and a back panel 1008 are provided to be opposed to each other with forming a discharge region 1013 therebetween. The discharge region 1013 is filled with a mixture gas, that is used as a discharge gas, composed of He, Ne, Xe, Ar and the like at a pressure not less than several hundreds of Torrs. At the bottom surface of the front panel 1001 provided at the side of a display surface, there is formed a pair of sustain discharge electrodes comprising X electrodes and Y electrodes placed in parallel to each other. A voltage is applied repeatedly to the pair of sustain discharge electrodes to cause a continuous emission. Generally, the X electrodes and the Y electrodes respectively are composed of transparent electrodes and opaque electrodes for supplementing a conductivity of the transparent electrodes. In other words, the X electrodes are composed of transparent X electrodes such as 1002-1 and 1002-2 and opaque bus X electrodes such as 1004-1 and 1004-2, while the Y electrodes comprises transparent Y electrodes such as 1003-1 and 1003-2 and opaque bus Y electrodes such as 1005-1 and 1005-2.
Each of the sustain discharge electrodes is coated with a front dielectric layer 1006, and a thin protection layer 1007 of magnesium oxide (MgO) or the like is formed on the front dielectric layer. MgO is high in secondary electron emission and serves to intensify a discharge at a collision with ions such as He, Ne, Xe and Ar that are generated by the discharge, thereby lowering a starting voltage. Further, MgO is excellent in sputtering resistance and, therefore, serves to protect the front dielectric layer 1006 from damages otherwise caused by a direct collision of the ions such as He, Ne, Xe and Ar generated by the discharge with the front dielectric layer 1006.
In turn, on upper surface of the back panel 1008, there are provided electrodes to write data for address discharge, or, address electrodes (hereinafter simply referred to as xe2x80x9cA electrodesxe2x80x9d) 1009 in an orthogonal direction with respect to the sustain discharge electrodes. Each of the A electrodes 1009 is coated with a back dielectric layer 1010, and ribs 1011 are provided on the back dielectric layer 1010 in such a manner as to sandwich the A electrodes 1009. Phosphors 1012 are applied on concaved regions, respectively, each of which is formed by wall surfaces of the ribs 1011 and an upper surface of the back dielectric layer 1010.
In above configuration, an intersection of the pair of sustain discharge electrodes and the A electrodes corresponds to a discharge cell region, and discharge cells are arranged in a matrix of about 1000xc3x9710000 in two dimensions. In the case of a color display, a pixel is composed of a three kinds of discharge cells respectively coated with red, green and blue phosphors.
An operation of a PDP will be described below.
A principle of emission of a PDP is such that a plasma comprising electrons and ions is generated from a discharge gas by means of a voltage applied to X and Y electrodes, and the electrons cause the discharge gas in a ground state to be in an excitation state, followed by converting ultraviolet rays generated from the discharge gas in the excitation state into visible rays by means of phosphors.
As shown in a block diagram of FIG. 11, the PDP 1100 is incorporated into the plasma display device 1102. A signal generator of pictures 1103 sends a signal indicating a display screen to a driving circuit 1101. The driving circuit 1101 receives and converts the signal into a voltage to be supplied to each of electrodes of the PDP 1100.
FIG. 12(A) explains a time chart of a voltage applied during a TV field period that is required for displaying an image on the PDP shown in FIG. 11. As shown in (I) in FIG. 12(A), a single TV field period 1200 is divided into subfields 1201 to 1208 that are different in a number of sustain voltage pulse application. Gradation is represented by adjusting the number of sustain voltage pulse application of each of the subfields, i.e., an intensity of emission caused by the sustain discharge. In the case of using 8 subfields each having a weight corresponding to an intensity of emission based on a binary scale, a discharge cell for tricolor display is capable of 28 (=256) gradations of brightness display, thereby making it possible to display about 16780000 colors. Each of the subfields has a period of reset discharge 1209 for restoring the discharge cell into an initial state, a period of address discharge 1210 for selecting an illuminated discharge cell and a period of sustain discharge 1211 for performing an emission display as shown in (II) of FIG. 12(A).
FIG. 12(B) shows applied voltage waveforms to be applied to the A, X and Y electrodes during the address discharge period 1210. The waveform 1212 is a voltage waveform applied to one of the A electrodes 1009 during the address discharge period 1210; 1213 and 1214 are voltage waveforms applied to i-th electrode and (i+1)th electrode of the Y electrodes; and the waveform 1217 is a voltage waveform applied to one of the X electrodes. Here, the applied voltages are respectively, V0, V21, V21 and V1 (V).
As shown in FIG. 12(B), in the case where a scan pulse 1215 is applied to i-th line of the Y electrodes, a discharge occurs between the Y electrodes and the A electrodes in a cell positioned at an intersection of the i-th line of the Y electrodes and the A electrodes 1009 of the voltage V0, and the discharge transfers from the Y electrodes to X electrodes to generate an address discharge. Such address discharge does not occur in a cell positioned at an intersection of the i-th line of the Y electrodes and the A electrodes 1009 to which the voltage V0 is not applied. The same applies to the case where a scan pulse 1216 is applied to the (i+1)th line of the Y electrodes. The cell at which the address discharge occurred, an electric charge generated by the discharge is formed as a wall charge on surfaces of the dielectric layer and the protection layer 1007 covering the X and Y electrodes, and a wall voltage Vw (V) occurs between the X electrodes and the Y electrodes. Presence or absence of a sustain discharge during the subsequent sustain discharge period 1211 hinges upon the presence or absence of the wall voltage.
FIG. 13(A) shows voltages waveforms applied simultaneously during the sustain discharge period 1211 of FIG. 12(A) between the X electrodes and the Y electrodes that are sustain discharge electrodes. An applied voltage waveform 1301 that is a voltage having a rectangular waveform is applied repeatedly to the Y electrodes and an applied voltage waveform 1302 that is a voltage having a rectangular waveform is applied repeatedly to the X electrodes. Each of the rectangular waveform serves to increase the voltage from 0 V to Vsus (V) in a rise period of a time 0 less than T less than Tr (s) when a time of a head of the waveform is 0. During a time Tr less than T less than Tr+Tsus (s), the voltage Vsus (V) is maintained. During a time Tr+Tsus less than T less than Tr+Tf+Tsus (s), the voltage Vsus (V) is lowered to 0V. During a time Tr+Tf+Tsus less than T less than Tr+Tf+Tsus+Tg (s), the voltage 0V is maintained.
In turn, in the A electrodes, a constant voltage Va (V) of an applied voltage waveform 1303 is applied from a time 0. The period of the time 0 less than T less than Tr+Tf+Tsus+Tg (s) becomes a cycle for a sustain discharge driving voltage, and the voltage of the rectangular waveform is applied alternately to the Y electrodes and the X electrodes.
The voltage value of the Vsus is so set that the absence or presence of the sustain discharge hinges upon the presence or absence of the wall voltage Vw that is a relative potential difference between the Y electrodes and the X electrodes caused by the address discharge. At the discharge cell where the address discharge occurs, it is so set that a sum of the wall voltage Vw and the sustain discharge voltage Vsus is larger than the starting voltage. In turn, at the discharge cell where the address discharge does not occur, it is so set that the sustain discharge voltage Vsus is lower than the starting voltage.
When one cycle of the sustain discharge driving voltage is finished, the relative potentials of the Y electrodes and the X electrodes are reversed to each other at the discharge where the address discharge occurred. When a second cycle of the sustain discharge driving voltage is applied between the sustain electrodes, the sum of the wall voltage Vw and the sustain discharge voltage Vsus exceeds the starting voltage again to repeat the discharge. Thus, a light emission continues for a period of time equivalent to the period of applying the sustain discharge driving voltage at the discharge cell whereat caused the address discharge, while no light emission occurs at a discharge cell where no address discharge is caused.
A emission efficiency of a presently available PDP is inferior to that of a cathode-ray tube, and it is necessary to improve the emission efficiency for the prevalence of a PDP as a home appliance. In the case of making a larger PDP, there is a problem that an electric power consumption increases with the increase in an electric current supplied to electrodes. To solve above problems, it is necessary to realize a PDP that achieves a high brightness with a lowered supply of electric current, thereby to improve the emission efficiency.
As techniques for improving the emission efficiency, an improvement in cell structure is proposed. For example, Japanese Patent Application Laid-open Nos. H8-315735, H8-22772 and H3-187125 propose a modification of a size or a form of a sustain discharge electrode. Japanese Patent Application Laid-open Nos. H8-315734 and H7-262930 propose a modification of a material of a dielectric that covers a sustain discharge electrode. Japanese Patent Application Laid-open No. H11-352927 proposes a modification of driving method, namely, a modification of a rectangular waveform into a driving waveform that is similar to an overshoot. Some of above techniques are put into practice; however, they do not reach the emission efficiency of the cathode-ray tube. In the improvement in the emission efficiency, it is especially difficult to improve an emission efficiency of ultraviolet rays and, therefore, the improvement is considered necessary as a break-through technique for developing the PDP as a home appliance.
The present invention is accomplished considering the above-described problems in the art, and an object of the present invention is to provide a plasma display device comprising a plasma display panel and a control method of applying a voltage on the plasma display device wherein the emission efficiency of ultraviolet rays is improved.
In order to achieve above object, the present invention provides a control method of applying a voltage on a plasma display device that displays an image by: structuring a discharge cell between a pair of a first electrode (Y or X electrode) and a second electrode (Y or X electrode) that is arranged in parallel to each other on a front panel and an address electrode to write data provided on a back panel; applying a sustain discharge voltage to each of the first and the second electrodes; and causing a discharge emission in the discharge cell to thereby display an image; wherein a discharge peak time of the discharge current is controlled by setting a voltage applied to the first and the second electrodes during a sustain discharge period to be a composite voltage which is a sum of the sustain discharge voltage and a variation voltage having a voltage larger than the sustain discharge voltage.
Further, the control method of applying a voltage on a plasma display device of the present invention comprises controlling the voltage applied to the address electrode in the sustain discharge electrode period to be a constant voltage or a voltage that is a sum of the constant voltage and a variation voltage. Further, the control method of applying a voltage on a plasma display device of the present invention comprises controlling the composite voltage to be a voltage having a waveform composed of an overshoot that is higher than the sustain discharge voltage and an over-dumping that is lower than the sustain discharge voltage.
Further, the present invention provides a plasma display device comprising a plasma display panel provided with a plurality of discharge cells in the form of a matrix each having a pair of a first electrode and a second electrode that are arranged in parallel to each other on a front panel and an address electrode to write data arranged on a back panel, a first driving circuit for applying a sustain discharge voltage to the first electrode, a second driving circuit for applying a sustain discharge voltage to the second electrode, a driving circuit to write data for applying a voltage to the address electrode, and a first variation voltage waveform generating circuit for adding a variation voltage to the sustain discharge voltage that is connected to each of the first and second driving circuits; wherein a composite voltage which is a sum of the sustain discharge voltage and the variation voltage is applied to each of the first and second electrodes.
The plasma display device according to the present invention comprises controlling the voltage applied from the driving circuit to write data to the address electrode to be a constant voltage or including a second variation voltage waveform generating circuit for adding the variation voltage to the constant voltage that is to be applied to the address electrode.
The plasma display device according to the present invention comprises an inductance circuit for controlling the composite voltage to be a voltage having a waveform composed of an overshoot that is higher than the sustain discharge voltage and an over-dumping that is lower than the sustain discharge voltage.
Further, the present invention provides a control method of applying a voltage on a plasma display device, comprising a plasma display panel having a plurality of discharge cells each comprising a pair of sustain discharge electrodes and an address electrode to write data for applying a voltage to at least one of the pair of sustain discharge electrodes and the address electrode during a sustain discharge period, the method comprising the steps of: applying to at least one of the pair of sustain discharge electrodes a sustain discharge voltage of a voltage waveform composed of a rise period (Tr) from a first voltage level to a second voltage level, a sustain period (Tsus) for maintaining the second voltage level, a fall period (Tf) from the second voltage level to the first voltage level and a sustain period (Tg) for maintaining the first voltage level, applying a constant voltage to the address electrode and applying to at least one of the pair of sustain discharge electrodes a composite voltage which is a sum of the sustain discharge voltage and a variation voltage during the rise period. Further, the control method of applying a voltage on a plasma display device of the present invention comprises controlling a main discharge peak time of a discharge current by controlling the composite voltage to be generated during the rise period and changing a time period during which the discharge voltage larger than the sustain discharge voltage is generated.
Further, the control method of applying a voltage on a plasma display device of the present invention comprises applying to the address electrode a voltage to which the variation voltage during a period where a time (T) is Tr+Tf+Tsus less than T less than Tr+Tf+Tsus+Tg is added.